This invention relates to industrial applications of ink jet recording heads, and more particularly to modifications in a liquid jetting structure wherewith improvements can be realized in the flight characteristics of the jetted liquid droplets such as linearity of advance and uniformity of liquid droplet quantities.
The performance of an ink jet recording head is greatly influenced by whether or not the nozzle or nozzles exhibit an affinity for the ink droplets. When the ink droplet jetting surface (i.e. the surface on the jetting side where the nozzle is open) exhibits high affinity for the ink, the ink droplets being jetted are pulled by adhering materials such as paper dust or ink remaining on the jetting surface, and are thus jetted in a bent direction that is not the originally planned jetting direction.
One conventional method for stabilizing the ink droplet jetting direction is to select the material of which the nozzle jetting surface is formed and treat the jetting surface to reduce the degree of ink affinity thereof. A publicized invention for forming nozzle surfaces of a self-aggregating monomolecular film is described in U.S. Pat. No. 5,598,193. According to this treatment method, the jetting surface exhibits hydrophobic properties toward ink, wherefore the ink droplets cease to be jetted in a bent direction.
With the conventional improvement technology described in the foregoing, however, even though the linearity of advance of the liquid droplets can be improved, the volume of liquid jetted from the nozzle or nozzles cannot be stabilized. Because the ink droplet volume is not stabilized, the volume of ink that adheres differs from one liquid droplet to another, so that, in some cases, high-quality printing cannot be done.
In cases where this ink jet recording head is used in industrial applications, in particular, instability in the liquid droplet volume ejected is a fatal flaw. Industrial applications of ink jet recording heads involve the formation of patterns by jetting not ink but liquids usable in industrial applications from nozzles of ink jet recording heads. In industrial applications wherein ink jet recording heads are used to form patterns, for example, the pitch widths in the patterns to be formed are very fine. Therefore, if the diameter of the liquid droplets jetted is not stabilized, fluctuations appear in the volume of adhering liquid, and patterns cannot be formed with stabilized widths.
This being so, in order to resolve the problems noted in the foregoing, a first object of the present invention is to provide a liquid jetting structure wherewith the linearity of advance of jetted liquid droplets can be enhanced and liquid droplet diameter stabilized.
A second object of the present invention is to provide an ink jet recording head that can be employed in industrial applications as a result of enhancing the linearity of advance of jetted liquid droplets and stabilizing the liquid droplet diameter.
A third object of the present invention is to provide a printer capable of printing with high print quality as a result of enhancing the linearity of advance of jetted liquid droplets and stabilizing the liquid droplet diameter.
In view of the problems noted in the foregoing, the inventor analyzed the behavior of liquids such as ink as they advance through a nozzle and are jetted as liquid droplets. As a result, the following facts were learned. As a liquid travels through the flow path of a nozzle, if the degree of affinity for the liquid suddenly declines, at that point of discontinuity, the liquid will separate from the surface of the walls configuring the flow path. The liquid that separates from the wall surface exhibits constriction as it advances further downstream. Then, due to surface tension, the liquid separates, with the significant point being the place of constriction, whereupon the leading portion becomes a liquid droplet and is jetted from the nozzle opening. If the velocity wherewith the liquid is advancing at this time is the same, the position where the significant point develops will be constant, and the diameter of the liquid droplets jetted will also be constant. Thereupon the inventor, using this behavior of liquids, conceived of a structure wherewith liquid droplets are generated stably while varying the degree of affinity of the flow path forming the nozzle.
In other words, the invention for realizing the first object noted above is a liquid jetting structure that, in a liquid jetting structure provided with nozzles for jetting a liquid, is characterized in that it comprises a nozzle (or nozzles) having a flow path wherein the degree of affinity for the liquid to be jetted is set so as to be different along the direction of liquid flow. The reason for this is that, when the degree of affinity for a liquid in a flow path is changed, the liquid separates from the surface of the flow path at that point of change and a significant point appears, and liquid droplets of uniform size are produced. This liquid jetting mechanism can be employed in all kinds of applications requiring uniform liquid droplets exhibiting good linearity of advance, such as in industrial manufacturing equipment, injectors and other medical equipment, and fuel injection apparatuses, in addition to nozzle components in ink jet recording heads.
By xe2x80x9cliquidxe2x80x9d here is meant not only ink, but any fluid exhibiting such viscosity that it can be jetted from a nozzle and used in industrial applications. This liquid may be either aqueous or oily. The liquid may also have prescribed mixture substances mixed therein in a colloidal form. By xe2x80x9cdegree of affinityxe2x80x9d is meant a value that can be determined by the size of the angle with which a surface contacts a liquid. The affinity for a liquid is determined relatively by the angle of liquid contact relative to a plurality of areas. In a flow path, for example, areas having small contact angles with the liquid become areas of relatively high affinity, while areas s having large contact angles with the same liquid become areas of relatively low affinity. Whether or not affinity is exhibited for a liquid is determined relatively by the relationship between the molecular structure of the liquid and the molecular structure of the flow path surface. Thus if the liquid is changed, the degree of affinity also changes. In cases where the liquid contains a polar molecule such as water, for example, comparatively high affinity, i.e. a hydrophilic property, will be exhibited if the molecules configuring the flow path surface exhibit a polar structure. If the molecules configuring the flow path surface film have a nonpolar structure, comparatively low affinity, i.e. water repellency, will be exhibited. Conversely, in cases where the liquid is basically configured of nonpolar molecules, as in an organic solvent, comparatively low affinity will be exhibited when the molecules configuring the flow path surface have a polar structure, and comparatively high affinity will be exhibited when the molecules configuring the flow path surface have a nonpolar structure. Accordingly, there will be cases where a flow path surface that exhibits comparatively high affinity for one liquid will exhibit comparatively low affinity for another liquid.
The flow path considered here, in more specific terms, is formed by a molecular film that is present as a thiolate in which a prescribed sulfur compound has been coagulated on a metal surface.
The sulfur compound mentioned above may be configured, for example, of a thiol compound represented by the chemical formula Rxe2x80x94SH where R is a hydrocarbon group. More specifically, if n, m, p, and q are any natural numbers, and X and Y are prescribed elements, then R may be represented by any of the following composition formulas, that is, by
CnH2n+1xe2x80x94,
CnF2n+1xe2x80x94,
CnF2n+1xe2x80x94CmH2mxe2x80x94,
CnF2n+1xe2x80x94(CH2)mxe2x80x94Xxe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x80x94Yxe2x80x94(CH2)pxe2x80x94
HO2C(CH2)nxe2x80x94,
HO(CH2)nxe2x80x94,
NC(CH2)nxe2x80x94,
H2n+1Cnxe2x80x94O2Cxe2x80x94(CH2)mxe2x80x94,
H3CO(CH2)nxe2x80x94,
X(CH2)nxe2x80x94(where X is a halogen element such as Br, Cl, or I, etc.)
H2Cxe2x95x90CH(CH2)nxe2x80x94
H3C(CH2)nxe2x80x94, or
CnF2n+1xe2x80x94(CH2)mxe2x80x94(NHCOxe2x80x94CH2)pxe2x80x94(CH2)qxe2x80x94.
The sulfur compound mentioned above may also be configured of a thiol molecule mixture represented by the mutually differing chemical structural formulas R1xe2x80x94SH and R2xe2x80x94SH where R1 and R2 represent different hydrocarbon groups. More specifically, R1 and R2 are represented by one of the following chemical structural formulas, that is, by
CnF2n+1xe2x80x94 or CnF2n+1xe2x80x94CmH2mxe2x80x94.
Alternatively, the sulfur compound mentioned above may be configured of a thiol compound represented by the chemical structural formula HSxe2x80x94R3xe2x80x94SH where R3 is a prescribed hydrocarbon group. More specifically, R3 may be represented by any of the following chemical structural formulas, namely by 
As another alternative, there are cases where, in the sulfur compound noted above, a thiol compound represented by the chemical structural formula R4xe2x80x94Sxe2x80x94Sxe2x80x94R4, where R4 is a prescribed hydrocarbon group, is formed, either partially or wholly. More specifically, if n, m, p, and q are any natural numbers and X and Y are prescribed elements, then R4 may be represented by any of the following chemical structural formulas, that is, by
CnH2n+1xe2x80x94,
CnF2n+1xe2x80x94,
CnF2n+1xe2x80x94CmH2mxe2x80x94,
CnF2n+1xe2x80x94(CH2)mxe2x80x94Xxe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94Yxe2x80x94(CH2)pxe2x80x94
HO2C(CH2)nxe2x80x94,
HO(CH2)nxe2x80x94,
NC(CH2)nxe2x80x94,
H2n+1Cnxe2x80x94O2Cxe2x80x94(CH2)mxe2x80x94,
H3CO(CH2)nxe2x80x94,
X(CH2)nxe2x80x94(where X is a halogen element such as Br, Cl, or I, etc.)
H2Cxe2x95x90CH(CH2)nxe2x80x94
H3C(CH2)nxe2x80x94, or
CnF2n+1xe2x80x94(CH2)mxe2x80x94(NHCOxe2x80x94CH2)pxe2x80x94(CH2)qxe2x80x94.
The flow path considered here is provided with a point of discontinuity where the degree of affinity for the liquid declines precipitously from the upstream end toward the downstream end.
This flow path, for example, is provided on the downstream end thereof with a region having a length of between 1 xcexc and 100 xcexc in which the degree of affinity for the liquid is relatively low.
In this flow path, furthermore, the degree of affinity for the liquid is set so that it gradually increases from the upstream end toward the downstream end thereof.
This flow path may also be provided on the downstream end thereof with a region wherein the degree of affinity for the liquid can be varied in response to changes in a physical quantity that is either heat, the strength of an electric field, or the strength of a magnetic field. When this is the case, means are also provided for supplying one of the physical quantities, that is, either heat, electric field strength, or magnetic field strength, in such manner that the quantity can be varied.
The jetting surface of the flow path noted above from which the liquid is jetted is set, for example, so that the degree of affinity for the liquid is relatively low.
Also, the inner surface of a reservoir for supplying the liquid to the flow path is set, for example, so that the degree of affinity for the liquid becomes relatively high.
The invention for achieving the second object noted earlier is an ink jet recording head that comprises the liquid jetting structure of the present invention. In terms of the jetting principle, a piezo jet mode, bubble jet mode, or static electric mode can be employed.
The invention for achieving the third object noted earlier is a printer comprising the ink jet recording head of the present invention.